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    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    

    <script>
        var myAtoi = function(str) {
            var newVal = "";
            if (new RegExp("^[ ]+$").test(str)) {
                return 0
            } else {
                if (str.length == 0) {
                    return 0 
                } else if (str.length == 1 && (str == "+" || str == "-")) {
                    return 0
                } else {
                    str = str.replace(/(^\s*)|(\s*$)/g, "");
                    for (var i = 0; i<str.length; i++) {
                        if (i == 0 && ( str[i] == "-" || str[i] == "+" || new RegExp("[0-9]+").test(str[i]) )) {
                            newVal += str[i]
                        } else if ( str[i] == "-" || str[i] == "+" || str[i] == ".") {
                            break
                        } else if (new RegExp("[0-9]+").test(str[i])) {
                            newVal += str[i]
                        } else if (i == 0 && /^[a-zA-Z]+$/.test(str[i])){
                            return 0
                        } else {
                            break
                        }
                    }
                }
               
            }

            if (newVal > 2147483648 - 1) {
                newVal = 2147483647
            } else if (newVal < -2147483648) {
                newVal = -2147483648
            }
            return newVal

        };

        // 空 "" 0
        // 空格 " " 0
        // +
        console.log(myAtoi("+-42"))
        // myAtoi("-135")
    </script>
</body>
</html>